Hi! We're also working on Heiretsu. Funnily enough, it uses the same compression algorithm that this game does (they're made by the same developer using the same SDK). I've actually done a ton of work making tooling for the game and we're basically ready to go, just lacking in translator manpower so we're completing Chokuretsu first. If you want to check out some of what we've written, you can see some of what we've done on our GitHub! https://github.com/haroohie-club/HeiretsuTranslationUtility

Reminds me of three projects of mine:

1. I reverse engineered the graphics format for the game Sopwith 2 so that I could change the sprites. I wanted to change the airplane into a flying ox: the ox was an obstacle in the game that you could crash into.

https://en.wikipedia.org/wiki/Sopwith_(video_game)

2. I reverse engineered the pattern format for the Dreamcast game "Samba de Amigo" so that I could add new songs.

3. I wrote a NES ROM editor with support to change sprites, text, and palettes. I was a junior in high school at that time. The code was a mess.